Please refer to FIG. 1A for an N-channel trench MOSFET 100 disclosed in a prior art of U.S. Pat. No. 8,587,054 having an N diffused drift region 101, wherein said N-channel trench MOSFET 100 is formed in an N-epitaxial layer 102 onto an N+ substrate 103. In FIG. 1A, a pair of deep trenches 104 are formed with each filled with: a pair of gate electrodes 105 and a shielded source electrode 106. In the mesa area between said pair of deep trenches 104, a P body region 107 and an N+ source region 108 is connected to a source metal through a trenched source-body contact region 109. FIG. 1B shows another cross-sectional view of the trench MOSFET 100 in FIG. 1A, the doping profile along A-B cross section is shown in FIG. 1C, which shows that, the N diffused drift region 101 has a higher doping concentration near the trench sidewalls of the deep trenches 104 than in center of the mesa area, which is easier to realize and control in process flow.
However, to fabricate the deep trenches 104 in FIG. 1A, it is hard to control the formation of the gate electrodes 105 and the shielded source electrode 106, especially in a small die size.
Therefore, there is still a need in the art of the semiconductor power device, particularly for trench MOSFET design and fabrication, to provide a novel cell structure, device configuration and fabrication process that would resolve these difficulties.